Patent application title: SOURCE DRIVER OF DISPLAY DEVICE, AND METHOD OF CONTROLLING THE SAME

Abstract:

A source driver having a cascade connection configuration that drives
signal lines of a display device according to a plurality of signals
transmitted by a mini-LVDS interface from a controller during a
predetermined period corresponding to a cascade signal received from a
preceding stage, the source driver including a first reception circuit
receiving a first signal of the plurality of signals; a second reception
circuit receiving a second signal of the plurality of signals; and an
enable control circuit that controls each of the first and second
reception circuits to one of an active state and a standby state; in
which the enable control circuit sets the second reception circuit to the
active state according to the cascade signal received from the preceding
stage, and sets the first and second reception circuits to the standby
state according to a cascade signal output by the source driver to a
subsequent stage.

Claims:

1. A source driver having a cascade connection configuration that drives
signal lines of a display device according to a plurality of signals
transmitted by a mini-LVDS interface from a controller during a
predetermined period corresponding to a cascade signal received from a
preceding stage, the source driver comprising:a first reception circuit
that receives a first signal of the plurality of signals;a second
reception circuit that receives a second signal of the plurality of
signals; andan enable control circuit that controls each of the first
reception circuit and the second reception circuit to one of an active
state and a standby state;wherein the enable control circuit sets the
second reception circuit to the active state according to the cascade
signal received from the preceding stage, and sets the first and second
reception circuits to the standby state according to a cascade signal
output by the source driver to a subsequent stage.

2. The source driver according to claim 1, whereinthe enable control
circuit sets the first reception circuit to the active state according to
a start signal, when the start signal to start the source driver is
received from the controller.

3. The source driver according to claim 2, whereinthe start signal is a
strobe signal output for every one horizontal period.

4. The source driver according to claim 1, whereinthe first signal that
the first reception circuit receives is a clock signal to generate an
operation clock of the source driver.

5. The source driver according to claim 1, whereinthe first signal that
the first reception circuit receives comprises a reset data signal to
reset the source driver.

6. The source driver according to claim 1, further comprising:a cascade
signal generation circuit that generates a cascade signal that the source
driver outputs to the subsequent stage after a predetermined period from
receiving a cascade signal from the preceding stage.

7. The source driver according to claim 1, whereinthe enable control
circuit comprises first and second RS latching circuit and selector,the
first RS latching circuit generates a first enable signal according to a
first pulse signal and a second pulse signal, the first pulse signal
supplied to a set terminal and corresponding to the start signal, the
second pulse signal supplied to a reset terminal and corresponding to a
cascade signal that the cascade signal generation circuit generates and
outputs to the subsequent stage,the second RS latching circuit generates
a second enable signal according to a third pulse signal and the second
pulse signal, the third pulse signal supplied to a set terminal and
corresponding to the cascade signal received from the preceding stage,
the second pulse signal supplied to a reset terminal,the selector selects
one of the first and second enable signals according to a select signal
based on the start signal and the cascade signal received from the
preceding stage and outputs the selected signal as a third enable
signal,the first enable signal controls the first reception circuit to
one of the active state and the standby state, andthe third enable signal
controls the second reception circuit to one of the active state and the
standby state.

8. A method of controlling a source driver that has a cascade connection
configuration and drives signal lines of a display device according to a
plurality of signals transmitted by a mini-LVDS interface from a
controller during a predetermined period when a cascade signal received
from a preceding stage is active, the source driver comprising:a first
reception circuit that receives a first signal of the plurality of
signals and a second reception circuit that receives a second signal of
the plurality of signals, the method comprising:setting the second
reception circuit to an active state according to the cascade signal
received from the preceding stage; andsetting the first and second
reception circuits to the standby state according to a cascade signal
output by the source driver to a subsequent stage.

Description:

INCORPORATION BY REFERENCE

[0001]This application is based upon and claims the benefit of priority
from Japanese patent application No. 2009-210478, filed on Sep. 11, 2009,
the disclosure of which is incorporated herein in its entirety by
reference.

BACKGROUND

[0002]1. Field of the Invention

[0003]The present invention relates to a source driver of a display device
and a method of controlling the same.

[0004]2. Description of Related Art

[0005]Recently, plane display devices such as a liquid crystal display
have been increased in size. A large-scale plane display device drives
signal lines by using an IC (Integrated Circuit) that is called a source
driver. The number of signal lines that can be driven by each source
driver has the limit. The plane display device that is enlarged and is
highly miniaturized has plural source drivers that have a cascade
connection configuration as shown in FIG. 6. The plane display device
sequentially operates plural source drivers, and drives all signal lines
for one horizontal line.

[0006]As shown in FIG. 6, a plane display device 1 of a related art
includes a controller 10, source drivers IC1 to IC4, and a display 12.
The controller 10 transmits a clock signal CLK, a loading signal LOAD,
and data signals DD0 to DD5 to each of source drivers. The clock signal
CLK is a signal to generate the operation clock of source drivers IC1 to
IC4. Data signals DD0 to DD5 are pixel data. Each of source drivers IC1
to IC4 outputs a pixel drive signal corresponding to data signals DD0 to
DD5 to the display 12. The loading signal LOAD is a strobe signal to
sequentially take data signals DD0 to DD5 into each of source drivers IC1
to IC4. This loading signal LOAD is output to source drivers IC1 to IC4
from the controller 10 for every horizontal period. In the example of
FIG. 6, the number of source drivers is limited to four for the
simplification of the drawing. However, a further number of source
drivers may be used.

[0007]Each of source drivers receives the clock signal CLK, the loading
signal LOAD, and data signals DD0 to DD5. Each of source drivers
sequentially latches data signals DD0 to DD5 that are pixel data. The
latch operation of each of source drivers is done according to a cascade
signal DOI from a preceding stage. The source driver IC1 receives a
logical signal of high level from a power-supply voltage terminal VDD as
the cascade signal DOI of the preceding stage.

[0008]As mentioned above, the plane display device has been enlarged and
highly miniaturized, and then the number of pixels of one horizontal line
has been increasing. Therefore, a high-speed forwarding of the data
signal and the like that is transmitted between the controller and each
source driver is needed. In a liquid crystal display, mini-LVDS is
generally used as an interface for a high-speed forwarding between this
controller and each source driver. The interface standard of this
mini-LVDS exchanges data and clock signals between a transmitting circuit
and a reception circuit with LVDS (Low voltage differential signaling)
shown in FIG. 7.

[0009]As shown in FIG. 7, the controller 10 includes a transmitting
circuit Tx, and each of source drivers IC1 to IC4 includes a reception
circuit Rx. FIG. 7 only shows the controller 10 and the source driver
IC1. The transmitting circuit Tx and the reception circuit Rx are
connected with signal buses LVDS+ and LVDS-. A differential signal is
transmitted to the signal buses LVDS+ and LVDS-. The transmitting circuit
Tx allows current to flow between the signal bus LVDS+, a terminator
resistor R1, and the signal bus LVDS-. Then, the reception circuit Rx
decides a logical value of the reception signal according to a polarity
of potential difference caused at both ends of the terminator resistor
R1. In such circuit configuration, noise reduction such as EMI (Electro
Magnetic Interference) is possible with a coupling between the signal
buses LVDS+ and LVDS-.

[0010]FIG. 8 shows a block diagram of each of source drivers IC1 to IC4.
The source drivers IC1 to IC4 have basically similar the configuration,
and thus only the configuration of the source driver IC1 will be
explained below. The source driver IC1 includes reception circuits RxDD0
to RxDD5, RxCLK, an enable control circuit 21, a divide-by-4 frequency
divider 22, a DOI signal generation circuit 23 and a data register 24.

[0011]Each of reception circuits RxDD0 to RxDD5, and RxCLK receives VLDS
signal from the controller 10 similarly to the reception circuit Rx of
FIG. 7. Reception circuits RxDD0 to RxDD5 and RxCLK receive data signals
DD0 to DD5 and the clock signal CLK that are VLDS signals, respectively.
Signals received by reception circuits RxDD0 to RxDD5 and RxCLK are
converted to CMOS signal level and are output to circuits provided at the
subsequent stage.

[0012]The enable control circuit 21 controls reception circuits RxDD0 to
RxDD5 and RxCLK to be in an active state or a standby state according to
an enable signal REC_EN. The configuration of the enable control circuit
21 is described later.

[0013]The divide-by-4 frequency divider 22 divides frequency of a clock
signal of CMOS signal level output by the reception circuit RxCLK by
four. The clock signal CLK whose frequency is divided by four is used as
an internal operation clock of the source driver IC1. Thus the source
driver IC1 decreases power consumption. Hereinafter, the clock signal
whose frequency is divided by four is called an internal operation clock
signal. The active state or the standby state of the divide-by-4
frequency divider 22 is controlled according to the enable signal REC_EN
of the enable control circuit 21.

[0014]Upon receiving a cascade signal DIO of high level, the DOI signal
generation circuit 23 outputs the cascade signal DOI of high level for a
predetermined period after a predetermined number of clocks. The DOI
signal generation circuit 23 includes a shift register 30. The shift
register 30 counts the clock signal CLK that is output by the reception
circuit RxCLK for predetermined number of clocks. One example of the
operation of the DOI signal generation circuit 23 will be briefly
explained below.

[0015]When the cascade signal DIO of high level is received, the DOI
signal generation circuit 23 makes the shift register 30 start to count
the number of clocks of the clock signal CLK. Then, when the shift
register 30 counts the predetermined number of clocks, the DOI signal
generation circuit 23 outputs the cascade signal DOI of high level for a
predetermined period. The predetermined period in which this cascade
signal DOI keeps the high level corresponds to, for instance, one cycle
of the operation clock.

[0016]Here, the configuration of the enable control circuit 21 is shown in
FIG. 9. As shown in FIG. 9, the enable control circuit 21 includes delay
circuits DLY1, DLY2, a NAND circuit NAND1, a NOR circuit NOR1, an
inverter circuit IV1, and an RS latching circuit RS1.

[0017]The delay circuit DLY1 includes inverter circuits IV11 to IV13. The
inverter circuits IV11 to IV13 that are sequentially connected with
series constitute an inverter chain. The inverter circuit IV11 of the
first stage receives the loading signal LOAD. Then, the inverter circuit
IV13 of the final stage outputs the loading signal LOAD delayed for a
predetermined period.

[0018]The NAND circuit NAND1 has one input terminal to which the loading
signal LOAD is input, and the other input terminal to which the loading
signal LOAD delayed for the predetermined period output by the inverter
circuit IV13 is input. The NAND circuit NAND1 outputs an operation result
to the inverter circuit IV1. The inverter circuit IV1 inverts the output
signal of the NAND circuit NAND1, and outputs the inverted signal as a
REC_SET signal. Therefore, the REC_SET signal is a pulse signal that is
in the high level by an amount of delay generated in the delay circuit
DLY1 from the rising edge of the loading signal LOAD.

[0019]The delay circuit DLY2 includes inverter circuits IV21 to IV23. The
inverter circuits IV21 to IV23 that are sequentially connected with
series constitute an inverter chain. The inverter circuit IV21 of the
first stage receives the cascade signal DOI. Then, the inverter circuit
IV23 of the final stage outputs the cascade signal DOI delayed for a
predetermined period.

[0020]The NOR circuit NOR1 has one terminal to which the cascade signal
DOI is input, and the other input terminal to which the cascade signal
DOI delayed for the predetermined period output by the inverter circuit
IV23 is input. The NOR circuit NOR1 outputs an operation result as a
REC_RSET signal. Therefore, the REC_RSET signal is a pulse signal that is
in the high level by an amount of delay generated in the delay circuit
DLY2 from the falling edge of the cascade signal DOI.

[0021]The RS latching circuit RS1 has a set terminal S to which the
REC_SET signal is input, and has a reset terminal R to which the REC_RSET
signal is input. Then, the RS latching circuit RS1 outputs an enable
signal REC_EN according to the REC_SET signal and the REC_RSET signal. In
detail, when receiving the REC_SET signal of high level, the RS latching
circuit RS1 outputs the enable signal REC_EN of high level from an output
terminal Q. Alternatively, when receiving the REC_RSET signal of high
level, the RS latching circuit RS1 outputs the enable signal REC_EN of
low level from the output terminal Q.

[0022]FIG. 10 shows a circuit configuration of reception circuits RxDD0 to
RxDD5 and RxCLK. The reception circuits RxDD0 to RxDD5 and RxCLK have
basically the similar configuration, and thus only the configuration of
the reception circuit RxDD0 will be explained below. As shown in FIG. 10,
the reception circuit RxDD0 includes PMOS transistors MP1 to MP6, NMOS
transistors MN1 to MN8, a NAND circuit NAND31, an inverter circuit IV31,
and a current supply CC31.

[0023]A differential stage is composed of the current supply CC31 and PMOS
transistors MP1 and MP2, and the NMOS transistor MN1. The differential
stage receives the LVDS signal. An amplifying stage is composed of PMOS
transistors MP3 to MP6 and NMOS transistors MN5 to MN8. The amplifying
stage amplifies the signal that is output from the above-mentioned
differential stage.

[0024]When the enable signal REC_EN is in the high level, the LVDS signal
becomes a signal at CMOS level and it is output from the reception
circuit RxDD0. On the other hand, when the enable signal REC_EN is in the
low level, NMOS transistors MN1 to MN4 interrupt current pathways between
a power-supply voltage terminal VDD and a voltage terminal VSS. Further,
an output of the NAND circuit NAND31 is fixed to the high level by the
enable signal REC_EN of low level. Therefore, an output of the inverter
circuit IV31, which is the output of the reception circuit RxDD0 is fixed
to the low level and the reception circuit RxDD0 is in the standby state.
Accordingly, the active state or the standby state of the reception
circuit RxDD0 is controlled according to the enable signal REC_EN.

[0025]FIGS. 11 to 13 show timing charts that show operation of source
drivers IC1 to IC4. Note that the same reference symbols of time in FIGS.
11 to 13 indicate the same time. In addition, it is assumed that
reception circuits RxCLK and RxDD0 to RxDD5 of all source drivers are in
the standby state before time t1.

[0026]The loading signal LOAD of high level is received by source drivers
IC1 to IC4 at time t1. In the enable control circuit 21 of each of source
drivers, the REC_SET signal of a pulse signal is generated according to
the rising edge of this loading signal LOAD. The enable signal REC_EN of
high level is output from the RS latching circuit RS1 according to this
REC_SET signal. Then, reception circuits RxCLK and RxDD0 to RxDD5 of each
of source drivers enter the active state according to this enable signal
REC_EN.

[0027]All source drivers receive data signal DD0 of high level as reset
data RST at time t2. In a mini-LVDS interface, after the reception
circuit Rx enters active state, the data signal DD0 that is in the high
level is set to the reset data RST for four cycles of the clock signal
CLK (period T1).

[0028]After receiving the reset data RST, the divide-by-4 frequency
divider 22 outputs the internal operation clock signal at time t3 in each
of all source drivers. Each source driver operates according to this
internal operation clock signal. Because the cascade signal DIO is in the
high level, the source driver IC1 starts taking data of data signals DD0
to DD5 at timings of rising and falling edges of the clock signal CLK.
Here, because the data is taken according to timings of rising and
falling edges of the clock signal CLK as mentioned above, the data of
eight bits is taken into the source driver IC1 in each one cycle of the
internal operation clock for each data signal line.

[0029]Here, when (m×6)/8 pixel signal lines (m is a multiple of
four) are driven for each one source driver, data taking of this one
source driver is completed at the m-th edge timing of the clock signal
CLK. Therefore, the source driver IC1 takes data of data signals DD0 to
DD5 at each edge of the clock signal CLK between the edge of the clock
signal CLK at time t3 (the first edge) and the edge of the clock signal
CLK at time t5 (the m-th edge).

[0030]The shift register 30 of the source driver IC1 counts the (m-3)-th
edge of the clock signal CLK at time t4. Then, the shift register 30
informs the DOI signal generation circuit 23 that the count reaches the
predetermined number. Then, at this timing the DOI signal generation
circuit 23 of the source driver IC1 raises the cascade signal DOI to the
high level. Note that the cascade signal DOI of this source driver IC1 is
the cascade signal DIO of the source driver IC2.

[0031]At time t7 after one cycle of the internal operation clock from time
t4, the DOI signal generation circuit 23 of the source driver IC1 lowers
the cascade signal DOI to the low level. In addition, the REC_RSET signal
of a pulse signal is generated by the enable control circuit 21 of the
source driver IC1 according to this falling edge. The enable signal
REC_EN of low level is output from the RS latching circuit RS1 according
to this REC_RSET signal. Then, reception circuits RxCLK and RxDD0 to
RxDD5 of the source driver IC1 enter the standby state according to this
enable signal REC_EN of low level. Moreover, the divide-by-4 frequency
divider 22 that generates the internal operation clock enters the standby
state, too. Therefore, the source driver IC1 enters the standby state.

[0032]On the other hand, the source driver IC2 that receives the cascade
signal DIO of high level starts to take data of data signals DD0 to DD5
at each edge of the clock signal CLK from the rising edge of the internal
operation clock at time t6. Note that the edge of the clock signal CLK at
time t6 is (m+1)-th edge. Therefore, the source driver IC2 takes data of
data signals DD0 to DD5 at each edge of the clock signal CLK between the
edge of the clock signal CLK at time t6 (the (m+1)-th edge) and the edge
of the clock signal CLK at time t9 (the 2 m-th edge). At the same time,
the shift register 30 of the source driver IC2 starts to count the edge
of the clock signal CLK at time t6.

[0033]The shift register 30 of the source driver IC2 counts the (m-3)-th
edge of the clock signal CLK at time t8. Then, the shift register 30
informs the DOI signal generation circuit 23 that the count reaches the
predetermined number. Then, at this timing the DOI signal generation
circuit 23 of the source driver IC2 raises the cascade signal DOI to the
high level. The cascade signal DOI of this source driver IC2 is the
cascade signal DIO of the source driver IC3.

[0034]At time t11 after one cycle of the internal operation clock from
time t8, the DOI signal generation circuit 23 of the source driver IC2
lowers the cascade signal DOI to the low level. In addition, the REC_RSET
signal of a pulse signal is generated by the enable control circuit 21 of
the source driver IC2 according to this falling edge. The enable signal
REC_EN of low level is output from the RS latching circuit RS1 according
to this REC_RSET signal. Then, reception circuits RxCLK and RxDD0 to
RxDD5 of the source driver IC2 enter the standby state according to this
enable signal REC_EN of low level. Moreover, the divide-by-4 frequency
divider 22 that generates the internal operation clock enters the standby
state, too. Therefore, the source driver IC2 enters the standby state.

[0035]After this, source drivers IC3 and IC4 perform the similar operation
as described above. More specifically, the source driver IC3 that
receives the cascade signal DIO of high level starts to take data of data
signals DD0 to DD5 at each edge of the clock signal CLK from the rising
edge of the internal operation clock at time t10. Note that the edge of
the clock signal CLK at time t10 is (2 m+1)-th edge. Therefore, the
source driver IC3 takes data of data signals DD0 to DD5 at each edge of
the clock signal CLK between the edge of the clock signal CLK at time t10
(the (2 m+1)-th edge) and the edge of the clock signal CLK at time t13
(the 3m-th edge). At the same time, the shift register 30 of the source
driver IC3 starts to count the edge of the clock signal CLK at time t10.

[0036]The shift register 30 of the source driver IC3 counts the (m-3)-th
edge of the clock signal CLK at time t12. Then, the shift register 30
informs the DOI signal generation circuit 23 that the count reaches the
predetermined number. Then, at this timing the DOI signal generation
circuit 23 of the source driver IC3 raises the cascade signal DOI to the
high level. The cascade signal DOI of this source driver IC3 is the
cascade signal DIO of the source driver IC4.

[0037]At time t15 after one cycle of the internal operation clock from
time t12, the DOI signal generation circuit 23 of the source driver IC3
lowers the cascade signal DOI to the low level. In addition, the REC_RSET
signal of a pulse signal is generated by the enable control circuit 21 of
the source driver IC3 according to this falling edge. The enable signal
REC_EN of low level is output from the RS latching circuit RS1 according
to this REC_RSET signal. Then, reception circuits RxCLK and RxDD0 to
RxDD5 of the source driver IC3 enter the standby state according to this
enable signal REC_EN of low level. Moreover, the divide-by-4 frequency
divider 22 that generates the internal operation clock enters the standby
state, too. Therefore, the source driver IC3 enters the standby state.

[0038]The source driver IC4 that receives the cascade signal DIO of high
level starts to take data of data signals DD0 to DD5 at each edge of the
clock signal CLK from the rising edge of the internal operation clock at
time t14. Note that the edge of the clock signal CLK at time t14 is (3
m+1)-th edge. Therefore, the source driver IC4 takes data of data signals
DD0 to DD5 at each edge of the clock signal CLK between the edge of the
clock signal CLK at time t14 (the (3 m+1)-th edge) and the edge of the
clock signal CLK at time t17 (the 4m-th edge). At the same time, the
shift register 30 of the source driver IC4 starts to count the edge of
the clock signal CLK at time t14.

[0039]The shift register 30 of the source driver IC4 counts the
(m-3)-th edge of the clock signal CLK at time t16. Then, the shift
register 30 informs the DOI signal generation circuit 23 that the count
reaches the predetermined number. Then, at this timing the DOI signal
generation circuit 23 of the source driver IC4 raises the cascade signal
DOI to the high level. The cascade signal DOI of this source driver IC4
is the cascade signal DIO of a source driver of the subsequent stage.

[0040]At time t19 after one cycle of the internal operation clock from
time t16, the DOI signal generation circuit 23 of the source driver IC4
lowers the cascade signal DOI to the low level. In addition, the REC_RSET
signal of a pulse signal is generated by the enable control circuit 21 of
the source driver IC4 according to this falling edge. The enable signal
REC_EN of low level is output from the RS latching circuit RS1 according
to this REC_RSET signal. Then, reception circuits RxCLK and RxDD0 to
RxDD5 of the source driver IC4 enter the standby state according to this
enable signal REC_EN of low level. Moreover, the divide-by-4 frequency
divider 22 that generates the internal operation clock enters the standby
state, too. Therefore, the source driver IC4 enters the standby state.

[0041]A technology of a liquid crystal display device that includes source
drivers having a cascade connection configuration is disclosed in
Japanese Unexamined Patent Application Publication No. 2005-284217.

SUMMARY

[0042]The present inventor has found a problem as described below. In the
plane display device 1 of the related art, the reception circuits RxCLK
and RxDD0 to RxDD5 of source drivers IC1 to IC4 are in the active state
from time t1 as shown in FIG. 11 to FIG. 13. This is due to the fact that
reception circuits RxDD0 and RxCLK which receive the clock signal CLK and
the reset data RST of each of source drivers enter the active state at
time t1 in the mini-LVDS interface standard.

[0043]However, source drivers IC1 to IC4 that are connected with cascade
connection need not make reception circuits RxDD1 to RxDD5 active other
than reception circuits RxDD0 and RxCLK until the cascade signal DIO of
high level is received. Therefore, in reception circuits RxDD1 to RxDD5,
unnecessary power is consumed. Moreover, even if a source driver is in
the standby state, power consumption of the source driver keeps
increasing in a liquid crystal display device or the like that is
enlarged and highly miniaturized. Therefore, it is necessary to reduce
wasting power consumption as mentioned above for the decrease of power
consumption of source drivers.

[0044]A first exemplary aspect of an embodiment of the invention is a
source driver having a cascade connection configuration that drives
signal lines of a display device according to a plurality of signals
transmitted by a mini-LVDS interface from a controller during a
predetermined period corresponding to a cascade signal received from a
preceding stage, the source driver including: a first reception circuit
that receives a first signal of the plurality of signals; a second
reception circuit that receives a second signal of the plurality of
signals; and an enable control circuit that controls each of the first
reception circuit and the second reception circuit to one of an active
state and a standby state; in which the enable control circuit sets the
second reception circuit to the active state according to the cascade
signal received from the preceding stage, and sets the first and second
reception circuits to the standby state according to a cascade signal
output by the source driver to a subsequent stage.

[0045]The source driver in accordance with an exemplary aspect of the
present invention sets the second reception circuit to the active state
according to the cascade signal received from the preceding stage. Then
the source driver sets the second reception circuit to the standby state
according to the cascade signal output by the source driver to the
subsequent stage. Therefore, the second reception circuit can enter the
standby state during a period in which the second reception circuit needs
not enter the active state in the source driver that has a cascade
connection configuration. Then, power consumption in the source driver
can be reduced during the period in which the second reception circuit
needs not enter the active state.

[0046]The power consumption can be reduced according to the source driver
in accordance with the exemplary aspect of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0047]The above and other exemplary aspects, advantages and features will
be more apparent from the following description of certain exemplary
embodiments taken in conjunction with the accompanying drawings, in
which:

[0048]FIG. 1 is an example of a configuration of a source driver in
accordance with an exemplary embodiment of the present invention;

[0049]FIG. 2 is an example of a configuration of an enable control circuit
of the source driver in accordance with the exemplary embodiment of the
present invention;

[0050]FIG. 3 is a timing chart for explaining operations of a display
device in accordance with the exemplary embodiment of the present
invention;

[0051]FIG. 4 is a timing chart for explaining operations of the display
device in accordance with the exemplary embodiment of the present
invention;

[0052]FIG. 5 is a timing chart for explaining operations of the display
device in accordance with the exemplary embodiment of the present
invention;

[0053]FIG. 6 is a configuration of a general display device;

[0054]FIG. 7 is a schematic diagram to explain an LVDS interface.

[0055]FIG. 8 is a configuration of a source driver of a related art;

[0056]FIG. 9 is a configuration of an enable control circuit of the source
driver of the related art;

[0057]FIG. 10 is a circuit configuration of a reception circuit.

[0058]FIG. 11 is a timing chart for explaining operations of a display
device of a related art;

[0059]FIG. 12 is a timing chart for explaining operations of the display
device of the related art; and

[0060]FIG. 13 is a timing chart for explaining operations of the display
device of the related art;

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Exemplary Embodiment

[0061]A specific exemplary embodiment of the present invention is
explained hereinafter with reference to the drawings. In this exemplary
embodiment, the present invention is applied to source drivers IC1 to IC4
of a liquid crystal display device. Note that a block configuration of
the liquid crystal display device of this exemplary embodiment is similar
to that shown in FIG. 6, and therefore explanation of the configuration
thereof is omitted here. Therefore, source drivers IC1 to IC4 in FIG. 6
are replaced by source drivers IC1 to IC4 in this exemplary embodiment.

[0062]FIG. 1 shows a block diagram of source drivers IC1 to IC4. Note that
the source drivers IC1 to IC4 have the similar configuration. Therefore,
only a configuration of the source driver IC1 will be explained in the
following description.

[0063]As shown in FIG. 1, the source driver IC1 includes reception
circuits RxDD0 to RxDD5, and RxCLK, an enable control circuit 100, a
divide-by-4 frequency divider 22, a DOI signal generation circuit 23 and
a data register 24. In FIG. 1, the configurations denoted by the same
reference symbols as in FIG. 8 indicate the same or similar
configurations as those therein. The enable control circuit 100 is
different between the source driver IC1 of FIG. 1 and the source driver
IC1 of FIG. 8. Thus the above different point is mainly described in this
exemplary embodiment.

[0064]As shown in FIG. 1, enable signals REC_EN1 and REC_EN3 described
later are output from the enable control circuit 100. The enable signal
REC_EN1 is supplied to reception circuits RxCLK and RxDD0. The enable
signal REC_EN3 is supplied to reception circuits RxDD1 to RxDD5.
Hereinafter, the enable control circuit 100, which is a feature part of
this invention, is mainly described in this exemplary embodiment.

[0065]FIG. 2 shows the configuration of the enable control circuit 100. As
shown in FIG. 2, the enable control circuit 100 includes delay circuits
DLY101, DLY111 and DLY121, NAND circuits NAND101 and 102, a NOR circuit
NOR101, inverter circuits IV101 and IV102, RS latching circuits RS101 and
RS102, a D flip-flop DFF101, and a selector SEL101.

[0066]The delay circuit DLY101 includes inverter circuits IV101 to IV103.
The inverter circuits IV101 to IV103 that are sequentially connected with
series constitute an inverter chain. The inverter circuit IV101 of the
first stage receives a loading signal LOAD. Then, the inverter circuit
IV103 of the final stage outputs the loading signal LOAD delayed for a
predetermined period.

[0067]The NAND circuit NAND has one input terminal to which the loading
signal LOAD is input, and the other input terminal to which the loading
signal LOAD delayed for the predetermined period output by the inverter
circuit IV103 is input. The NAND circuit NAND outputs an operation result
to the inverter circuit IV101. The inverter circuit IV101 inverts the
output signal of the NAND circuit NAND101, and outputs the inverted
signal as a REC_SET1 signal. Therefore, the REC_SET1 signal is a pulse
signal that is in high level by an amount of delay generated in the delay
circuit DLY101 from the rising edge of the loading signal LOAD.

[0068]The delay circuit DLY111 includes inverter circuits IV111 to IV113.
The inverter circuits IV111 to IV113 that are sequentially connected with
series constitute an inverter chain. The inverter circuit IV111 of the
first stage receives a cascade signal DOI. Then, the inverter circuit
IV113 of the final stage outputs the cascade signal DOI delayed for a
predetermined period.

[0069]The NOR circuit NOR101 has one input terminal to which the cascade
signal DOI is input, and the other input terminal to which the cascade
signal DOI delayed for the predetermined period output by the inverter
circuit IV113 is input. The NOR circuit NOR101 outputs an operation
result as a REC_RSET signal. Therefore, the REC_RSET signal is a pulse
signal that is in the high level by an amount of delay generated in the
delay circuit DLY111 from the falling edge of the cascade signal DOI.

[0070]The delay circuit DLY121 includes inverter circuits IV121 to IV123.
The inverter circuits IV121 to IV123 that are sequentially connected with
series constitute an inverter chain. The inverter circuit IV121 of the
first stage receives a cascade signal DIO. Then, the inverter circuit
IV123 of the final stage outputs the cascade signal DIO delayed for a
predetermined period.

[0071]The NAND circuit NAND102 has one input terminal to which the cascade
signal DIO is input, and the other input terminal to which the cascade
signal DIO delayed for the predetermined period output by the inverter
circuit IV123 is input. The NAND circuit NAND102 outputs an operation
result to the inverter circuit IV102. The inverter circuit IV102 inverts
the output signal of the NAND circuit NAND102, and outputs the inverted
signal as a REC_SET2 signal. Therefore, the REC_SET2 signal is a pulse
signal that is in the high level by an amount of delay generated in the
delay circuit DLY121 from the rising edge of the cascade signal DIO.

[0072]The RS latching circuit RS101 has a set terminal S to which the
REC_SET1 signal is input, and has a reset terminal R to which the
REC_RSET signal is input. Then, the RS latching circuit RS101 outputs an
enable signal REC_EN1 according to the REC_SET1 signal and the REC_RSET
signal. In detail, when receiving the REC_SET1 signal of high level, the
RS latching circuit RS101 outputs the enable signal REC_EN1 of high level
from an output terminal Q. When receiving the REC_RSET signal of high
level, the RS latching circuit RS101 outputs the enable signal REC_EN1 of
low level from the output terminal Q.

[0073]The RS latching circuit RS102 has a set terminal S to which the
REC_SET2 signal is input, and has a reset terminal R to which the
REC_RSET signal is input. Then, the RS latching circuit RS102 outputs an
enable signal REC_EN2 according to the REC_SET2 signal and the REC_RSET
signal. In detail, when receiving the REC_SET2 signal of high level, the
RS latching circuit RS102 outputs the enable signal REC_EN2 of high level
from the output terminal Q. When receiving the REC_RSET signal of high
level, the RS latching circuit RS102 outputs the enable signal REC_EN2 of
low level from the output terminal Q.

[0074]The D flip-flop DFF101 has a data input terminal D to which the
cascade signal DIO is input, and a clock input terminal to which the
loading signal LOAD is input. The D flip-flop DFF101 latches the cascade
signal DIO according to the rising edge of the loading signal LOAD. Then,
the value that the D flip-flop DFF101 latches is output from a data
output terminal Q as a CHIP--1 signal.

[0075]Because the cascade signal DIO is always in the high level
(power-supply voltage VDD), the D flip-flop DFF101 of the source driver
IC1 outputs a CHIP--1 signal of high level according to a timing
that the loading signal LOAD is raised up to high level. The D flip-flop
DFF101 of each of source drivers IC2 to IC4 outputs a CHIP--1 signal
of low level at a timing that the loading signal LOAD is raised up to
high level because the cascade signal DIO is in the low level.

[0076]The selector SEL101 has one input terminal to which the enable
signal REC_EN1 is input, and the other input terminal to which the enable
signal REC_EN2 is input. Then, the selector SEL101 selects one of enable
signals REC_EN1 and REC_EN2, and outputs the select signal as the enable
signal REC_EN3. In detail, when the CHIP--1 signal is in the high
level (the value is "1"), the enable signal REC_EN1 is output as the
enable signal REC_EN3. Alternatively, when the CHIP--1 signal is in
the low level (the value is "0"), the enable signal REC_EN2 is output as
the enable signal REC_EN3. As described above, it is only the source
driver IC1 that the CHIP--1 signal is in the high level. Therefore,
only the source driver IC1 outputs the enable signal REC_EN1 as the
enable signal REC_EN3. In the other source drivers IC2 to IC4, the enable
signal REC_EN2 is outputs as the enable signal REC_EN3.

[0077]As mentioned above, the enable control circuit 100 outputs enable
signals REC_EN1 and REC_EN3. Reception circuits RxCLK and RxDD0 receive
the enable signal REC_EN1, and reception circuits RxDD1 to RxDD5 receive
the enable signal REC_EN3. Therefore, an active state and a standby state
of reception circuits RxCLK and RxDD0 are controlled according to the
enable signal REC_EN1. Further, an active state and a standby state of
reception circuits RxDD1 to RxDD5 are controlled according to the enable
signal REC_EN3.

[0078]FIG. 3 to FIG. 5 show timing charts that show the operation of
source drivers IC1 to IC4 that include the enable control circuit 100 in
this exemplary embodiment. Note that the same reference symbols of time
in FIGS. 3 to 5 indicate the same time. In addition, it is assumed that
reception circuits RxCLK and RxDD0 to RxDD5 of all source drivers are in
the standby state before time t1.

[0079]The loading signal LOAD of high level is received by source drivers
IC1 to IC4 at time t1. In the enable control circuit 100 of each of
source drivers, the REC_SET1 signal of a pulse signal is generated
according to the rising edge of this loading signal LOAD. The enable
signal REC_EN1 of high level is output from the RS latching circuit RS101
according to the REC_SET1 signal. Then, reception circuits RxCLK and
RxDD0 of each of all source drivers enter the active state according to
this enable signal REC_EN1.

[0080]Moreover, the CHIP--1 of the source driver IC1 is in the high
level at this time t1. The selector SEL101 selects the enable signal
REC_EN1. Therefore, the enable signal REC_EN3 of the source driver IC1
becomes the enable signal REC_EN1 of high level as mentioned above.
Therefore, reception circuits RxDD1 to RxDD5 of the source driver IC1
enter the active state. On the other hand, the CHIP--1 of source
drivers IC2 to IC4 are in the low level. Therefore, the enable signal
REC_EN3 of the source drivers IC2 to IC4 becomes the enable signal
REC_EN2 of low level as mentioned above. Therefore, reception circuits
RxDD1 to RxDD5 of the source drivers IC2 to IC4 are in the standby state.

[0081]The reception circuits RxDD0 of all source drivers receive a data
signal DD0 of high level as a reset data RST at time t2. In a mini-LVDS
interface, after the reception circuit Rx enters the active state, the
data signal DD0 that is in the high level is set to the reset data RST
for four cycles of the clock signal CLK (period T1). After receiving the
reset data RST, the divide-by-4 frequency divider 22 outputs an internal
operation clock signal at time t3 in each of all source drivers. Each
source driver operates according to this internal operation clock signal.

[0082]Because the cascade signal DIO is in the high level, the source
driver IC1 starts taking data of data signals DD0 to DD5 at timings of
rising and falling edges of the clock signal CLK. Here, because the data
is taken according to timings of rising and falling edges of the clock
signal CLK as mentioned above, the data of eight bits is taken into the
source driver in each one cycle of the internal operation clock for each
data signal line.

[0083]Here, when (m×6)/8 pixel signal lines (m is a multiple of
four) are driven for each one source driver, data taking of this one
source driver is completed at the m-th edge timing of the clock signal
CLK. Therefore, as shown in FIG. 3, the source driver IC1 takes data of
data signals DD0 to DD5 at each edge of the clock signal CLK between the
edge of the clock signal CLK at time t3 (the first edge) and the edge of
the clock signal CLK at time t5 (the m-th edge).

[0084]The shift register 30 of the source driver IC1 counts the (m-3)-th
edge of the clock signal CLK at time t4. Then, the shift register 30
informs the DOI signal generation circuit 23 that the count reaches the
predetermined number. Then, the DOI signal generation circuit 23 of the
source driver IC1 raises the cascade signal DOI to the high level at this
timing. Note that the cascade signal DOI of this source driver IC1 is the
cascade signal DIO of the source driver IC2.

[0085]At time t7 after one cycle of the internal operation clock from time
t4, the DOI signal generation circuit 23 of the source driver IC1 lowers
the cascade signal DOI to the low level. In addition, the REC_RSET signal
of a pulse signal is generated by the enable control circuit 100 of the
source driver IC1 according to this falling edge. The enable signal
REC_EN1 of low level is output from the RS latching circuit RS101
according to this REC_RSET signal. Then, reception circuits RxCLK and
RxDD0 of the source driver IC1 enter the standby state according to this
enable signal REC_EN1 of low level. In addition, the enable signal
REC_EN1 of low level is output from the selector SEL101 as the enable
signal REC_EN3. Therefore, reception circuits RxDD1 to RxDD5 enter the
standby state as well as the reception circuits RxCLK and RxDD0 mentioned
above. Moreover, the divide-by-4 frequency divider 22 that generates the
internal operation clock enters the standby state, too. Therefore, the
source driver IC1 enters the standby state.

[0086]On the other hand, the source driver IC2 receives the cascade signal
DIO of high level at time t4. In the enable control circuit 100 of the
source driver IC2, the REC_SET2 signal of a pulse signal is generated
according to the rising edge of this cascade signal DIO. The enable
signal REC_EN2 of high level is output from the RS latching circuit RS102
according to this REC_SET2 signal. Here, the CHIP--1 signal of the
source driver IC2 is in the low level as state above. Therefore, the
selector SEL101 selects the enable signal REC_EN2. In other words,
REC_EN2=REC_EN3. Therefore, the enable signal REC_EN3 of the source
driver IC2 also rises to the high level, and the reception circuits RxDD1
to RxDD5 of the source driver IC2 enter the active state.

[0087]After that, the source driver IC2 that receives the cascade signal
DIO of high level starts to take data of data signals DD0 to DD5 at each
edge of the clock signal CLK from the rising edge of the internal
operation clock at time t6. Note that the edge of the clock signal CLK at
time t6 is (m+1)-th edge. Therefore, the source driver IC2 takes data of
data signals DD0 to DD5 at each edge of the clock signal CLK between the
edge of the clock signal CLK at time t6 (the (m+1)-th edge) and the edge
of the clock signal CLK at time t9 (the 2 m-th edge). At the same time,
the shift register 30 of the source driver IC2 starts to count the edge
of the clock signal CLK at time t6.

[0088]The shift register 30 of the source driver IC2 counts the
(m-3)-th edge of the clock signal CLK at time t8. Then, the shift
register 30 informs the DOI signal generation circuit 23 that the count
reaches the predetermined number. Then, at this timing the DOI signal
generation circuit 23 of the source driver IC2 raises the cascade signal
DOI to the high level. Note that the cascade signal DOI of this source
driver IC2 is the cascade signal DIO of the source driver IC3.

[0089]At time t11 after one cycle of the internal operation clock from
time t8, the DOI signal generation circuit 23 of the source driver IC2
lowers the cascade signal DOI to the low level. In addition, the REC_RSET
signal of a pulse signal is generated by the enable control circuit 100
of the source driver IC2 according to this falling edge. The enable
signal REC_EN1 of low level is output from the RS latching circuit RS101
according to this REC_RSET signal. Moreover, the enable signal REC_EN2 of
low level is output from the RS latching circuit RS102 with the REC_RSET
signal. Then, reception circuits RxCLK and RxDD0 of the source driver IC2
enter the standby state according to this enable signal REC_EN1 of low
level. Moreover, the enable signal REC_EN2 of low level is output from
the selector SEL101 as the enable signal REC_EN3. Therefore, reception
circuits RxDD1 to RxDD5 enter the standby state as well as the reception
circuits RxCLK and RxDD0 mentioned above. Moreover, the divide-by-4
frequency divider 22 that generates the internal operation clock enters
the standby state, too. Therefore, the source driver IC2 enters the
standby state.

[0090]After this, source drivers IC3 and IC4 perform the similar operation
as the source driver IC2. More specifically, as shown in FIG. 4 (and FIG.
3), the source driver IC3 receives the cascade signal DIO of high level
at time t8. Then, in the enable control circuit 100 of the source driver
IC3, the REC_SET2 signal of a pulse signal is generated according to the
rising edge of this cascade signal DIO. The enable signal REC_EN2 of high
level is output from the RS latching circuit RS102 according to this
REC_SET2 signal. Because the CHIP--1 signal of the source driver IC3
is in the low level, the selector SEL101 selects the enable signal
REC_EN2. Therefore, REC_EN2=REC_EN3. Accordingly, the enable signal
REC_EN3 of the source driver IC3 also rises to the high level, and the
reception circuits RxDD1 to RxDD5 of the source driver IC3 enter the
active state.

[0091]Further, in the source driver IC3 that receives the cascade signal
DIO of high level starts to take data of data signals DD0 to DD5 at each
edge of the clock signal CLK from the rising edge of the internal
operation clock at time t10. Note that the edge of the clock signal CLK
at time t10 is (2 m+1)-th edge. Therefore, the source driver IC3 takes
data of data signals DD0 to DD5 at each edge of the clock signal CLK
between the edge of the clock signal CLK at time t10 (the (2 m+1)-th
edge) and the edge of the clock signal CLK at time t13 (the 3m-th edge).
At the same time, the shift register 30 of the source driver IC3 starts
to count the edge of the clock signal CLK at time t10.

[0092]The shift register 30 of the source driver IC3 counts the
(m-3)-th edge of the clock signal CLK at time t12. Then, the shift
register 30 informs the DOI signal generation circuit 23 that the count
reaches the predetermined number. Then, at this timing the DOI signal
generation circuit 23 of the source driver IC3 raises the cascade signal
DOI to the high level. Note that the cascade signal DOI of this source
driver IC3 is the cascade signal DIO of the source driver IC4.

[0093]At time t15 after one cycle of the internal operation clock from
time t12, the DOI signal generation circuit 23 of the source driver IC3
raises the cascade signal DOI fall to the low level. In addition, the
REC_RSET signal of a pulse signal is generated by the enable control
circuit 100 of the source driver IC3 according to this falling edge. The
enable signal REC_EN1 of low level is output from the RS latching circuit
RS101 according to this REC_RSET signal. Moreover, the enable signal
REC_EN2 of low level is output from the RS latching circuit RS102 with
the REC_RSET signal. Then, reception circuits RxCLK and RxDD0 of the
source driver IC3 enter the standby state according to this enable signal
REC_EN1 of low level. Moreover, the enable signal REC_EN2 of low level is
output from the selector SEL101 as the enable signal REC_EN3. Therefore,
reception circuits RxDD1 to RxDD5 enter the standby state as well as the
reception circuits RxCLK and RxDD0 mentioned above. Moreover, the
divide-by-4 frequency divider 22 that generates the internal operation
clock enters the standby state, too. Therefore, the source driver IC3
enters the standby state.

[0094]Further, as shown in FIG. 5 (and FIG. 4), the source driver IC4
receives the cascade signal DIO of high level at time t12. Then, in the
enable control circuit 100 of the source driver IC4, the REC_SET2 signal
of a pulse signal is generated according to the rising edge of this
cascade signal DIO. The enable signal REC_EN2 of high level is output
from the RS latching circuit RS102 according to this REC_SET2 signal.
Because the CHIP--1 signal of the source driver IC4 is in the low
level, the selector SEL101 selects the enable signal REC_EN2. Therefore,
REC_EN2=REC_EN3. Accordingly, the enable signal REC_EN3 of the source
driver IC4 also rises to the high level, and the reception circuits RxDD1
to RxDD5 of the source driver IC4 enter the active state.

[0095]Further, in the source driver IC4 that receives the cascade signal
DIO of high level starts to take data of data signals DD0 to DD5 at each
edge of the clock signal CLK from the rising edge of the internal
operation clock at time t14. Note that the edge of the clock signal CLK
at time t14 is (3 m+1)-th edge. Therefore, the source driver IC4 takes
data of data signals DD0 to DD5 at each edge of the clock signal CLK
between the edge of the clock signal CLK at time t14 (the (3 m+1)-th
edge) and the edge of the clock signal CLK at time t17 (the 4 m-th edge).
At the same time, the shift register 30 of the source driver IC4 starts
to count the edge of the clock signal CLK at time t14.

[0096]The shift register 30 of the source driver IC4 counts the (m-3)-th
edge of the clock signal CLK at time t16. Then, the shift register 30
informs the DOI signal generation circuit 23 that the count reaches the
predetermined number. Then, at this timing the DOI signal generation
circuit 23 of the source driver IC4 raises the cascade signal DOI to the
high level. Note that the cascade signal DOI of this source driver IC4 is
the cascade signal DIO of a source driver of the subsequent stage.

[0097]At time t19 after one cycle of the internal operation clock from
time t16, the DOI signal generation circuit 23 of the source driver IC4
lowers the cascade signal DOI to the low level. In addition, the REC_RSET
signal of a pulse signal is generated by the enable control circuit 100
of the source driver IC4 according to this falling edge. The enable
signal REC_EN1 of low level is output from the RS latching circuit RS101
according to this REC_RSET signal. Moreover, the enable signal REC_EN2 of
low level is output from the RS latching circuit RS102 with the REC_RSET
signal. Then, reception circuits RxCLK and RxDD0 of the source driver IC4
enter the standby state according to this enable signal REC_EN1 of low
level. Moreover, the enable signal REC_EN2 of low level is output from
the selector SEL101 as the enable signal REC_EN3. Therefore, reception
circuits RxDD1 to RxDD5 enter the standby state as well as the reception
circuits RxCLK and RxDD0 mentioned above. Moreover, the divide-by-4
frequency divider 22 that generates the internal operation clock enters
the standby state, too. Therefore, the source driver IC4 enters the
standby state.

[0098]Here, as shown in FIG. 11 to FIG. 13, in the plane display device 1
of a related art, reception circuits RxCLK and RxDD0 to RxDD5 of the
source drivers IC1 to IC4 are in the active state from time t1. This is
due to the fact that reception circuits RxDD0 and RxCLK which receive the
clock signal CLK and the reset data RST of each of source drivers enter
the active state at time t1 in the mini-LVDS interface standard.

[0099]However, source drivers IC1 to IC4 need not make reception circuits
RxDD1 to RxDD5 active other than reception circuits RxDD0 and RxCLK until
the cascade signal DIO of high level is received. Nevertheless, in the
plane display device 1 of the related art, reception circuits RxDD1 to
RxDD5 are continuously set to the active state from time t1. Therefore,
in reception circuits RxDD1 to RxDD5, unnecessary electric power is
consumed.

[0100]However, in source drivers of the plane display device in this
exemplary embodiment, reception circuits RxDD1 to RxDD5 can be set to the
standby state until the cascade signal DIO of high level is received by
each of source drivers because each of source drivers has the enable
control circuit 100 that has the configuration as described above.
Therefore, the power consumption of the source driver in this exemplary
embodiment can be decreased compared with that of the related art.

[0101]Note that the present invention is not limited to the above
exemplary embodiment but can be modified as appropriate within the scope
of the present invention. For example, the interface between the
transmitting circuit and the reception circuit is not limited to the
mini-LVDS. For example, in the above-mentioned exemplary embodiment, the
reception circuit RxDD0 is in the active state from time t1 in all source
drivers since the reception circuit RxDD0 receives the reset data RST.
However, the reception circuit RxDD0 may enter the standby state until
the cascade signal DIO of high level is received as is similar to
reception circuits RxDD1 to RxDD5 when it is not required to comply with
such protocol.

[0102]While the invention has been described in terms of several exemplary
embodiments, those skilled in the art will recognize that the invention
can be practiced with various modifications within the spirit and scope
of the appended claims and the invention is not limited to the examples
described above.

[0103]Further, the scope of the claims is not limited by the exemplary
embodiments described above.

[0104]Furthermore, it is noted that, Applicant's intent is to encompass
equivalents of all claim elements, even if amended later during
prosecution.